Manufacture of cellulose from straw



gated cardboard and the like.

Patented Nov. 3, 1931 "UNITED STATES PATENT OFFICE ELTON R. DARLING, OF DANITILLE, ILLINOIS, ASSIG-NOR, BY MESNE ASSIGNMENTS, TO

CORNSTALK PRODUCTS COMPANY, INC., OF

DELAWARE No Drawing.

ufacture paper from straw and to employ in this process various alkaline media in order to remove the hemi-cellulosic constituents from the straw so as to liberate the fibers therefrom. Almost universally, the alkali used has been some form of lime, usually milk of lime, and the process has been carried out either at ordinary-or at superatmospheric pressure. The cellulose resulting from the old processes invariably was strongly tinged with yellow, and in some cases was almost brown, and no amount of bleachin was effective in removing this undesira le color with the result that paper and cardboard made from straw had both alimited application and was suitable only for the manufacture of cheap wrapping paper and of corru- Many attempts have been made to overcoine the inherent difliculties in the conversion ofstraw into a white paper, but no workable process of any commercial possibility has been available.

One ofthe objects ofmy invention is to overcome the difficulties above enumerated,

- andto produce from anyetype of straw, such as wheat straw, rice straw, oat straw, and the like, a cellulose that is brilliantly white, very high in alpha cellulose, and entirely suitable fer the manufacture of paper or' for admixture with pulp of other origin, or for the production of cellulose esters.

Ajfurther object of my invention ist treat'straw' with a chemical agent prior to the pulping operation proper, so as to convert-the therein contained non-cellulosic constituents into a material that may be sub-' NEW YORK, N. Y., A CORPORATION OF MANUFACTURE OF CELLULOSE FROM STRAW Application filed December 13, 1928. Serial No. 325,890.

sequently removed by appropriate treatment.

A further object of my invention is to treat straw with a dilute solution of a nitrogen acid, so as to change some of the non-cellulosic, as well as certain of the cellulosic constituents thereof and to render the same soluble in dilute alkalies so as to allow of their subsequent removal.

Other objects of my invention will be evident from the specification and claims hereinbelow set forth.

In carrying out my improved process in accordance with my present invention, I proceed substantially as follows:

The straw, which may, for example, be wheat straw, is first chopped or cut into lengths of approximately one-half inch. It is then threshed or dusted to remove loosely adhering foreign material, such as sand, dead insects, and so forth, this operation being done While the straw is in the dry state. The dusted straw is thereupon placed into a solution of a nitrogen acid, as, for example, nitric acid, or nitrous acid, or equivalents thereof, such as, for example, a mixture of sodium nitrate and sulphuric acid, sodium nitrite and hydrochloric acid or sulphuric acid; or a solution of fuming nitric acid which consists of a mixture of nitrous and nitric acid; or a solution of the fumes resulting from the oxidation of ammonia gas, which, as will be understood, when dissolved in water forms mostly nitric acid. However I do not wish to limit myself to any particular form of nitrogen acid, although I employ as the most readily available and inexpensive, the ordi nary nitric acid commercially available.

. The strength of the acid used by me is substantially equal to 2% of actual HNO in water. This solution is contained in either a stone ware or enamel lined vessel or any other vessel capableof withstanding the action of the 2% acid solution. Straw is added to thissolution in the ratio of one part straw to eight parts of solution, whereupon themixture of straw and acid is heated to the boiling point. This may be accomplished by stone warecoils or by suitable enamelled or coated'iron pipes,

I so treated that the nitric acid will no, attack boiling is continued for approximately one hour. However, I may, alternatively, carry out this process under more than atmospheric pressure with 1% nitric acid, or else carry on.

the process in the open with 1% nitric acid by extending the time of treatment. If a closed tank is used, it should be lined with acid-proof tile or brick. in order to prevent corrosion of the vessel by the nitric acid.

The only visible action produced by boiling the straw with the nitric acid is a very marked lightening of the color of the straw, while the liquid assumes a reddish brown or dark brown color. However, the straw does not change'its original shape in any manner whatsoever, and is not broken down or digested or altered otherwise than has been hereinabove indicated. I am aware that nitric acid has been used in pressure boiling operations for the liberation of fiber from straw, but in the concentrations and the length of time I employ the nitric acid no pulping of the straw or disintegration takes place. The change in color from the original yellow of the straw to the lighter color, I believe is due to a superficial nitration or oxidation of some of the hemi-cellulosic constituents of the straw. I also believe that the beta and gamma cellulose is so altered as to render the same soluble in the dilute alkali subsequently used in the process.

After the solution and the straw have been boiled the required length of time, as, for example one hour in a 2% nitric acid solution, I interrupt the boiling and drain away the solution from the straw, for example through a false bottom in the tank in which the operations take place. The straw is then treated with a volume of water equivalent to that used for the boiling operation, which water is then drained away and replaced by a second volume of water in which the straw is allowed to soak for some time, whereupon the water is withdrawn. It will be found that the two changes of water will have removed practically entirely the nitric acid from the straw and the same will be substantially neutral. The treated straw is then put through a process of pulping in accordance with the process described in'my co-pendinglapplication Serial No. 325,894, which is the one used by me for the manufacture of cellulose from cornstalks and similar plants. This stage of the process is exactly the same as that disclosed in my said co-pending application and hence neednot be described herein. I may state, however, that the process comprises boiling the treated straw with a caustic soda solution of 1% strength containing also of 1% of sodium sulphite, the operation being carried out at a pressure of from 10 to 30* lbs. superatmospheric.

The cellulose resulting from the treatment.

as the treatment of the straw with nitric'acid followed by the alkaline boil as above indicated, is of a very light gray color and may be employed without any bleaching for the manufacture of a low grade paper. However, and contrary to all previous practice, I find that this light gray straw cellulose is amenable to bleaching byordinary hypochlorite and requires less of the hypochlorite than any type of cellulose of similar nature, and when so subjected to a bleach becomes brilliantly. white, so that high grade paper may be manufactured therefrom. An analysis of this bleached straw cellulose discloses the fact that it consists almost entirely of alpha-cellulose and will withstand the action of 17.5% sodium hydroxide for 30 minutes at 60 C. The alpha-cellulose content is on the order of 90% or better. Such alpha-cellulose is eminently suitable forthe manufacture of various cellulose esters such as cellulose nitrate, or acetate and the production of cellulose ethers, as well as high-grade paper.

While I have described my invention in connection with nitric acid, I wish it to be un' derstood that any other nitrogen acid will be suitable for the same purpose. I do not believe that the action ispurely one ofoxidation as I find that perchlorates and chlorates which act quite similar to the nitrogen or nitric acids, will not accomplish the results such as I have indicated. The process may be carried out in any suitable type of apparatus, provided only that the solution containing the acid may be heated-to the boiling point while acting upon the straw What I claim as new is:

1. The process of preparing straw for fiber liberation which comprises boiling the same with nitric acid of substantially 2% strength equivalent to I-INO 2. The process of preparing straw for fiber liberation which comprises boiling the same wlth a nitrogen acid of substantially 2% strength equivalent to I-INO and washing the straw free from said acid.

3. The process of preparing'straw for fiber llberation which comprises boiling the same with nitric acid of substantially 2% strength equivalent to HNO and washing the straw free from said acid.

fl. The process of preparing a cellulose hlgh 1n alpha-cellulose content from straw which comprises boiling the same with a nitrogen acid of substantially 2% strength equivalent to .HNO under conditions avoiding the liberation of oxides of nitrogen and physical disintegration of the straw, washing the same free from said acid and thereupon digesting the treated straw with an alkaline solution to liberate the fiber therefrom.

5. The process of preparing a cellulose high in alpha-cellulose content from straw which comprises boiling the same with nitric acid of substantially 2% strengthequivalent to I-INO under conditions avoiding the liberation of oxides of nitrogen and physical straw disintegration of the straw, washing the free from said acid and thereupon digesting the treated straw with an alkaline'solution to liberate the fiber therefrom.

In Witness whereof, I have hereuntd subscribed my name.

ELTON R. DARLING. 

